1. Field of the Invention
The present invention relates to machine tools and, in particular, to the sealing of boring spindles.
2. Description of the Prior Art
The sealing of boring spindles is presently done either with seals having elastic lips (made of rubber derivatives or of plastic materials), or with baffles, or with conventional faced ring seals.
The problem posed by boring spindles are of three types:
(a) the need for the best possible seal for preventing the entry of external agents (fluids or solids) into the bearings, and the consequent leakage of lubricants, PA1 (b) the reduction of the power dissipated by friction to a minimum value in order to avoid heating of the spindle, detrimental to the precision of the latter, PA1 (c) reduction to a minimum of the external overhang of the bearings (on the tool-holder side and on the drive pulley side), in order to increase the rigidity of the spindle and, consequently, its precision. PA1 (a) by the maintaining in contact of two flats (faces) assuring, on the one hand, complete sealing and, on the other, three degrees of freedom of the seal thus constituted (rotation, radial slippage, and going out of true), PA1 (b) by the selection of materials of low coefficient of friction and of high resistance to wear, PA1 (c) by the use, to ensure permanent contact of the ring faces, of a metal diaphragm spring under constraint concentric with the faces, thereby limiting the axial thickness of the sealing systems to the thickness of the faced rings, or essentially that of a lip seal or of a set of baffles, PA1 (d) finally, by using a static O-ring seal of standard type to transmit the force exerted by the diaphragm to the faced ring assembly, there are provided simultaneously, static sealing of the device, prevention of rotation of one of the faced rings, centering of the latter with respect to the axis of rotation and compensation of any imprecision in the assembly.
None of the solutions presently utilized responds totally to these three points. Actually, the seal with lips lead to much friction, difficulties in centering with respect to the axis of rotation, and much wear of the contacting parts; the baffles provide only imperfect sealing; finally, the conventional faced ring seals entail considerable axial bulk.